Control of a steam zone

ABSTRACT

In a rising steam flood thermal recovery process wherein viscous crude oil is recovered from a subsurface earth formation which comprises an upper predominately oil saturated zone and a lower predominately water saturated zone by injecting hot water and/or steam into the lower predominately water saturated zone through an injection well and producing fluids from the formation through a production well, a method for controlling the movement of steam within the formation by selectively plugging back the injection and producing wells.

United States Patent Bowman et al.

[ CONTROL OF A STEAM ZONE [72] Inventors: Ronald W. Bowman, Houston, Tex. 77042; Alvin Lee Hall, Boston, Mass. 02163 [73] Assignee: Shell Oil Company, New York,

[22] Filed: March 5, 1971 [21] Appl. No.: 121,384

[52] US. Cl. ..166/252, 166/272, 166/303 [51] Int. Cl. ..E2lb 43/20, E2lb 43/24 [58] Field of Search ..l66/252, 268, 272, 285, 303

[56] References Cited UNITED STATES PATENTS 2,923,356 2/1960 Glass 166/285 3,167,120 1/1965 Pryor ..l66/272 X 3,302,710 2/1967 Odel ..l66/252 X [451 Aug. 8, 1972 3/1968 Satter ..l66/272 4/1969 Durie ..l66/272 Primary Examiner-Robert L. Wolfe Attomey-l-larold L. Denkler and Theodore E. Bieber ABSTRA' CT In a rising steam flood thermal recovery process wherein viscous crude oil is recovered from a subsurface earth formation which comprises an upper predominately oil saturated zone and a lower predominately water saturated zone by injecting hot water and/or steam into the lower predominately water saturated zone through an injection well and producing fluids from the formation through a production well, a method for controlling the movement of steam within the formation by selectively plugging back the injection and producing wells.

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R. W. Bowman A. L. Hui! /N VENTORS PATENTEDAUB 81972 SHEET 2 0F 2 R W. Bowman A. L. Hall INVEN TORS CONTROL OF A STEAM ZONE 1. Field of the Invention This invention relates to a thermal recovery method for producing oil from a subsurface earth formation;

more particularly, the invention relates to a method forcontrolling the steam zone in a rising steam flood.

2. Description of the Prior Art In many areas of the world, reservoirs of low A.P.I. gravity crude oil exist which are diflicult to produce because the high viscosity of such oils makes them substantially immobile within the reservoir. It is well known that the mobility of such oil may be improved by heating the oil as by injecting steam or hot water into the reservoir. However, in some viscous oil reservoirs the oil may be so viscous and immobile at the naturally occuring reservoir temperature that it is difficult or impossible to initiate a steam and/r hot water flood in the formation by injecting a hot aqueous fluid into a predominately oil saturated portion of the formation.

Some of these reservoirs have predominately water saturated intervals or zones near the bottom of the reservoir. In such reservoirs, steam or hot water flooding may be initiated by first injecting hot aqueous fluid into the lower predominately water saturated zone to conductively heat the oil entrained in the adjacent upper zone. When the oil in this upper zone is sufficiently heated, the hot fluid is injected into the upper zone to drive the heated, more mobile oil to a producing well. Unfortunately, in some cases, the hot aqueous fluid moves quite rapidly through the water saturated zone from the injection well to the producing well. At a time usually long before the oil zone is adequately heated to accept injected fluid, steam breaks through to the producing well. This inhibits hydrocarbon entry into the well bore and causes steam locking in the production.

Such steam breakthrough into the producing wells has been previously combated primarily by cutting back the rate of hot fluid injection into the lower water saturated zone after detrimental production effects are observed. This approach has had the disadvantage that once steam has broken through to a producing well, a preferential path or fluid movement from the injection well to the producing well is established. .Fluid moves along this path quite rapidly and even when fluid injection is significantly reduced, some steam will usually reach the well bore of producing well and detrimentally affect the operation of the pump in that well.

SUMMARY OF THE INVENTION It has now been discovered that improved recovery of oil may be achieved in a steam flood wherein a water zone is utilized as a conduit to conductively heat an oil zone by controlling the movement of the steam zone to prevent steam breakthrough and consequential detrimental results therefrom by measuring either subsurface or surface produced fluid temperature and, when measured temperature indicates that steam breakthrough is imminent, plugging back the lower portion of the producing well. Thus, the producing well is plugged back before detrimental effects of steam breakthrough are encountered and, as is hereinafter described, while the oil production from that well is rising. Such a plugback forces the hot aqueous fluids to pass upward through more of the oil saturated section producing pump. The result is greatly decreased oil before entering the well bore. This lowers the temperature of the produced fluid and improves pump efficiencies. The overall effect is an increase in oil production, and a reduction in total heat produced.

As the steam zone continues to rise into the oil zone, temperature of produced fluid is monitored and more of the productive interval is plugged back as necessary when the measured temperature indicates that steam breakthrough is imminent. These plugbacks may be accomplished by filling a portion of the well bore with gravel and placing a cement cap on top.

The steam zone is caused to rise through the productive interval by the plugback techniqueuntil the oil in the oil zone has been sufficiently preheated and mobilized to make the injection of steam directly into this zone practical. At this time the lower portion of the injection well, which communicates with the predominately water saturated portion of the oil bearing formation, can be plugged off and steam injection commenced directly into the predominately oil saturated portion of the formation. This steam moves across the formation to the producing well further mobilizing and driving oil. from the formation into the producing well.

BRIEF DESCRIPTION OF THE DRAWING FIG. I shows a subsurface earth formation having an upper predominantly oil saturated zone and a lower predominantly water saturated zone which formation is being treated according to a rising steam flood technique wherein. heat is initially carried into the formation in injecting hot water and/or steam into the lower predominantly water saturated interval.

FIG. 2 shows, the formation of FIG. 1 after the producing well has been plugged back a first time.

. FIG. 3 shows the formation of FIG. 1 after the producing well has been plugged back a second time.

FIG. 4 shows the formation of FIG. 1 after the injection well has beenplugged back.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the figures we see a subsurface earth formation 10 of sandstone or other porous and permeable material. Within the formation 10 there is an upper predominantly oil saturated zone 11 and a lower predominantly water saturated zone 12. These zones initially meet an oil water contact 13.

The formation 10 is penetrated by an injection well 14 and a producing well 15. Wells 14 and 15 are completed in fluid communication with the oil zone and at least the upper portion of the water zone 12. For example, the wells 14 and 15 can be completed with a tubular casing 16 and 17 cemented in place with cement 18 and 19 and perforated across the formation 10 with perforations 20 and 21. It should be understood that the wells 14 and 15 may also be completed by other conventional techniques.

The producing well 15 is suitably equipped for withdrawing fluid from the formation 10. For example, a string of tubing 22 can extend from the surface into the well 15 to carry fluid pumped by a down-hole piston-type pump 23 to the surface. The pump 23 may be driven from a surface drive means (not shown) connected in driving relationship with pump 23 by means of rod string 24.

the highly viscous oil in the upper zone 11 is essentially immobile at reservoir conditions of temperature and pressure, the injected aqueous fluid initially moves into the predominantly water saturated zone 12. In the figures, the arrows 25 indicated typical channels of predominant injected fluid flow within the formation 10. As can be seen in FIG. 1 the injected aqueous fluid moves into the formation predominantly through the water zone 12. Assteam moves into the formation from the well 14 heat is transferred from the steam to the formation and the fluids contained therein and the steam eventually condenses to water. The line 26 in FIG. 1 defines the position of a steam-containing zone within the formation 10 after a period of injection. As indicated in the figure, while the predominant movement of injected aqueous fluid is through the water zone 12 from the injection well 14 to the producing a well 15, some steam does tend to rise into the oil zone 11 heating and mobilizing oil which then drains in a j counter-current direction into the lower predominantly, water saturated zone 12. In the figure, the shading 27' indicates portions of the formation of intermediate fluid saturation, ie the shaded zone 27 has an oil saturation higher than the original oil saturation of the predominantly water saturated zone 12 but lower than the original oil saturation of the predominantly oil saturated zone ll. As the mobilized oil drains from the steam zone 26 into the flowing stream of aqueous fluid '26 this oil is entrained and carried to the producing well 15.

As steam injection the formation 10. As the zone 26 moves toward the producing well 15, .the temperature of the fluid produced through the well 15, which is predominantly or may be determined by calculation from the measured temperature of the fluid at the surface. When this downhole temperature approaches a certain critical value, the lower portion of the well 15 is plugged back. The critical temperature is the boiling point of water at the minimum pressure encountered by the produced fluid in or entering the pump 23. Clearly the boiling point can vary from well to well depending upon pressure conditions in the formation 10 and producing well 15. In many wells, at the subsurface pump this temperature falls in the range of about 300F to 340F. To obtain highly beneficial results, the plug-back is effected when downhole fluid temperature is between about F and 509F below the critical temperatureThis means that the well 15 isplugged back before detrimentalproduction effects are encountered and while oil-production is increasing.

7 into the formation 10 through well 14 continues the steam zone 26 moves'farther into FIG. 2 shows the well 15 after it has been plugged back with a plug 29. The plug 29 may comprise pea gravel sealed at the top by a 1-3 foot cement cap, or may be a conventional swab cup pack-off. The well is advantageously pluggedback to a point above the oil water contact to cause hot injected fluid to move into the upper zone 11 before entering the well 15. We have also found that it is advantageous for the plugged-off portion of the well to be at least 10 feet long to prevent steam or hot water coning into the well.

- As shown in FIG. 2, the plug 29 causes the fluid flow to pass through more of the oil zone 11 before reaching the well 15. This lowers the temperature of produced fluidand allows steam injection into the injection well 14 to be continued ata relatively high rate. The tem-' perature of produced fluid is still frequently measured after plug 29 has been placed in the producing well. If the critical temperature is reached again before the entire oil zone 11 has. been heated sufficiently to allow fluid injectiondirectly into the oil zone 11, then the well is pluggedback again with a second plug 30-as shown in FIG. 3. The plug 30 causes the path of fluid flow 25 to be diverted even higher into the oil zone 1 1, l2.

The plugback technique is continued until the entire oil zone 11' is heated to a temperature sufficient to. allow fluid to be injected into the oil zone 11. The particular temperature at which suchinjection becomes practical will vary from field to field depending upon the temperature-viscosity relationship of the oil in the formation and upon the flow properties of the reservoir rock. Those skilled in the art will be able to determine the particular temperature of the upper zone 11 at which that zone is in proper condition for fluid injection. At this time the injection well 14 is plugged back to the wateroil contact or above as illustrated in FIG.

' 4, thus diverting injected fluid directly into the oil zone l l to drive oil to the producing well 15. I

We claim as our invention 1. In a hot aqueous flood of an oil containing forma- I fluid reaches a selected value which indicates that steam breakthrough into the producing well is imminent but before steam breakthrough occurs, plugging back the lower portion of the producing well to cause the hot fluid to rise into the oil zone. 2. The method of claim 1 wherein the producing well is provided with a subsurface pump and wherein the selected value of measured temperature of the produced fluid is about 340F at the pump.

3. The method of claim 1 including the steps of: continuing injection of hot fluid into the water zone to conductively heat the oil zone and mobilize the oil therein; thereafter plugging back the lower portion of the injection well to a point adjacent the oil zone; and injecting steam through the injection well into the oil zone to displace oil from the oil zone.

face earth formation having an upper predominantly oil saturated zone and a lower predominantly water saturated zone comprising the steps of: I

providing at least two wells which are opened into fluid communication with the oil zone and the water zone of the formation; injecting a hot aqueous fluid through a first of these wells and into the water zone; producing fluid from the formation through the second of the wells by pumping the fluid with a subsurface pump; measuring the temperature of the produced fluid;

when the measured temperature of the produced the subsurface purnp, plugging back the producing well to a point above the original contact between the upper predominantly oil saturated zone and the lower predominantly water saturated zone; thereafter continuing to inject 'hot aqueous fluid through the first well and continuing to produce fluid from the formation through the second well. 5. The method of claim 4 wherein the selected tem perature is about 350F;

6. The method of claim 4 includingthe steps of after plugging back the producing well;

continuing to measure the temperatures of the produced fluid from the producing well; and when the measured temperature of the produced fluid again reaches the selected value, again plugging back the producing Iwell. 

1. In a hot aqueous flood of an oil containing formation wherein a water zone is utilized as a conduit for passing hot fluid from an injection well to a producing well to conductively heat an adjacent, overlying oil zone, a method for controlling the movement of hot fluid through the formation which comprises: measuring the produced fluid temperature; and when the measured temperature of the produced fluid reaches a selected value which indicates that steam breakthrough into the producing well is imminent but before steam breakthrough occurs, plugging back the lower portion of the producing well to cause the hot fluid to rise into the oil zone.
 2. The method of claim 1 wherein the producing well is provided with a subsurface pump and wherein the selected value of measured temperature of the produced fluid is about 340* F at the pump.
 3. The method of claim 1 including the steps of: continuing injection of hot fluid into the water zone to conductively heat the oil zone and mobilize the oil therein; thereafter plugging back the lower portion of the injection well to a point adjacent the oil zone; and injecting steam through the injection well into the oil zone to displace oil from the oil zone.
 4. A method of producing viscous oil from a subsurface earth formation having an upper predominantly oil saturated zone and a lower predominantly water saturated zone comprising the steps of: providing at least two wells which are opened into fluid communication with the oil zone and the water zone of the formation; injecting a hot aqueous fluid through a first of these wells and into the water zone; producing fluid from the formation through the second of the wells by pumping the fluid with a subsurface pump; measuring the temperature of the produced fluid; when the measured temperature of the produced fluid indicates that the temperature of fluid in the well at the subsurface pump has reached a selected value less than the boiling point of water entering the subsurface pump, plugging back the producing well to a point above the original contact between the upper predominantly oil saturated zone and the lower predominantly water saturated zone; thereafter continuing to inject hot aqueous fluid through the first well and continuing to produce fluid from the formation through the second well.
 5. The method of claim 4 wherein the selected temperature is about 350* F.
 6. The method of claim 4 including the steps of after plugging back the producing well; continuing to measure the temperatures of the produced fluid from the producing well; and when the measured temperature of the produced fluid again reaches the selected value, again plugging back the producing well. 